Advances in technology have resulted in smaller and more powerful computing devices. For example, there currently exist a variety of portable personal computing devices, including wireless computing devices, such as portable wireless telephones, personal digital assistants (PDAs), and paging devices that are small, lightweight, and easily carried by users. More specifically, portable wireless telephones, such as cellular telephones and Internet Protocol (IP) telephones, can communicate voice and data packets over wireless networks. Further, many such wireless telephones include other types of devices that are incorporated therein. For example, wireless telephones can also include a digital still camera, a digital video camera, a digital recorder, and an audio file player. Also, such wireless telephones can process executable instructions, including software applications, such as a web browser application, that can be used to access the Internet. As such, these wireless telephones can include significant computing capabilities.
Digital signal processors (DSPs), image processors, and other processing devices are frequently used in portable personal computing devices that include digital cameras, or that display image or video data captured by a digital camera. Such processing devices can be utilized to provide video and audio functions, to process received data such as image data, or to perform other functions.
Latency and accuracy are quality measures of an autofocus (AF) system of a digital camera. Latency may be inversely proportional to a frame rate of the digital camera, where the frame rate is usually given in frames per second (FPS). Accuracy may be related to the autofocus search algorithm, as well as to random errors that affect sharpness statistics. Conventionally, in low light conditions, exposure control will typically increase the exposure time to reduce the noise effect and will, therefore, decrease the frame rate and increase hand-shake blur of a handheld digital camera. However, the decreased frame rate will increase the autofocus latency, while the hand-shake blur or jitter will reduce the accuracy of the sharpness statistics and, thus, adversely affect the final autofocus accuracy.